Hawking structures his discussion of the
beginning of time, by describing progressively more accurate models of
the Universe. He begins with the ancient, geocentric models,
continuing to the more familiar steady-state and big bang models as he
relates discoveries that required new models of the universe. Galileo’s discovery that moons orbited Jupiter forced a heliocentric
model of the universe and Newton’s theory of an attractive
gravitational force and Hubble’s discovery that of the red shift in
galaxies ultimately forced an expansionistic model.

After a discussion of Einstein’s theory of relativity, which says that
the speed of light is always constant and therefore, there is no
absolute time (and, indeed, time and space are interrelated), Hawking
discusses in more detail modern models of the Universe. Hubble’s
discovery, along with fact that the Universe appears pretty much
identical in all directions (verified by the constant microwave
radiation from the early Universe discovered later) determined that the
Universe was expanding. There were some attempts to avoid a
beginning of time, but ultimately, general relativity implies that
there must be a beginning of time.

Next is a discussion of quantum mechanics and the uncertainty
principle. Quantum mechanics views particles as probability
waves, so one can never measure both a particle’s velocity and location
exactly. After this there is a discussion of elementary
particles, namely that all particles appear to be made of quarks, which
come in six flavors, each with three colors. Each particle is
composed of three quarks and comes is four varieties of spin: 1/2, 0, 1, and 2. Spin 1/2 particles make up matter, spin 0
particles; the rest are massless particles that are
manifestations of the four fundamental forces. Spin 1 particles
are photons (electromagnetism), bosons (weak nuclear force) and gluons
(strong nuclear force). Spin 2 particles are gravitons
(gravity). Theories have been developed that unify the spin 1
forces but cannot be verified because the forces unify at incredibly
high energies. It turns out, though, that particles can decay
into other particles (generally particles and antiparticles), and while
this is mostly symmetric, there is a slight bias in favor of particles.

With this information, black holes can now be discussed. Black
holes are created by stars larger than a certain size whose mass is so
large that gravity is stronger than all of the other forces and it
collapses into a singularity when it dies. As one approaches the
singularity, there is an event horizon, beyond which not even light can
pass. At the singularity, the laws of physics break down, due to
the infinities involved there. When this happens, time ceases to
have a meaning and we cannot perform useful analysis. This would
cause similar problems with the beginning of the Universe, if it began
with a singularity.

Quantum mechanics becomes important here. Because the energy
density of space cannot be exactly zero due to the uncertainty
principles, virtual particles and antiparticles are constantly being
created. Usually these must annihilate, giving a net 0
energy. However, if the antiparticle falls into a black hole, the
particle is free to continue its existance (or vice-versa), effectively
sucking energy from the black hole. The smaller the black hole,
the easier it is for the particle to escape, so small black holes
radiate more energy than large ones, possibly ending life in a big
explosion. Non-uniform densities of matter in the early Universe
may have formed black holes smaller than those from stars and some of
them may actually be decaying in our time. No such decay has been
observed, which gives an upper limit on how non-uniform the early
Universe was—apparently it was very smooth.

The usual model of the Universe states that temperature is inversely
proportional to size. So at the beginning, when the singularity
had no area, it was infinitely hot. One second afterwards, it had
cooled enough to allow photons, electrons, and neutrinos. One
hundred seconds after the beginning protons and neutrons began
condensing into nuclei of hydrogen, helium, and other light
elements. After a few hours this would have stopped. Nothing would have happend for the next million years as the Universe
expanded enough to cool down to the point where atoms could form
(several thousand degrees). At this point stars could begin to
form.

There are some difficult questions that this model raises,
however. First, why was the early Universe so hot (i.e. why is
temperature inversely proportional to size)? Second, why is the
Universe so uniform (at large scales)? Since light has not been
able propogate between all regions of the Universe, no communication
could have happened for the density to become uniform, so it must have
started that way. This is surprising, since a non-uniform density
seems so much more probable. Third, why did the universe expand
at almost exactly the critical rate for it to always expand? This
required great precision at the beginning, again unlikely. How
did the local irregularities (i.e. the galaxies) form from the
uniformity? Unfortunately, since the laws of physics break down
at singularities, general relativity cannot answer these questions.

Some of these questions can be answered by the anthropic principle,
which come in two flavors. The weak anthropic principle says that
a large system like the Universe is likely to have conditions for
sentient life in few areas, so we should not be surprised that we live
in on of those areas. The strong anthropic principle says that we
see the Universe as it is, because if it were otherwise, we would not
be here to see it. It would be preferable, though, to know that
many different intial conditions would give rise to results similar to
what we see. This would happen if there is a spin 0 field. High densities would have a repulsive force and would expand faster
than low densities, which would smooth them out.

We still cannot look beyond the singularity, but Hawking proposes that
we may be able to get around the problem with quantum theory. Since we do not have a viable theory unifying quantum theory and
gravity, this is a bit speculative. But we do know that such a
theory requires summing of the probabilities and that space-time must
be curved. In order for us to be able to do the mathematics,
space-time must be imaginary, in which case it might be curved similar
to the Earth. The Earth is “flat” and has finite area, but has no
boundaries. If this model is correct, the Universe would have no
boundary condition, i.e. no beginning. “The universe would be
completely self-contained and not affected by anything outside
itself. It would neither be created nor destroyed. It would
just BE.”

Hawking finishes with a description of why the arrow of time must
always point in the future for sentient beings, discusses string theory
as a possible unifying theory, and notes that complicated life can only
exist in three dimensions: in two dimensions the digestive tract
and circulatory system separates the organism, and in dimensions larger
than three gravity falls off too rapidly with distance to permit stable
orbits. He finishes with “if we do discover a complete [unifying]
theory, ... it would be the ultimate triumph of human reason—for then
we would know the mind of God.”

A Brief History of Time is a
very readable explanation of complicated physics. Hawking
explains the relevant laws of physics as part of a coherent plan
leading to his main discussion, always giving a quick background of how
these theories came to be. The explanations are simple, accurate,
well-illustrated, and peppered with short insights into the character
of the discoverer. In fact, the explanations are so good that
readers with a background in Physics will likely find that their
understanding of the concepts increases, particularly in why it is the
way it is.

Christian readers will likely find themselves both intriuged and
disturbed. While he admits that our knowledge is not sufficient
to label his ideas of the Universe as God as anything other than
proposals, they are mathematically compelling, even to those who
believe that God is more personal than a mathematical Universe can
be. An intellectually honest person must consider arguments that
his views are correct and Hawking’s suggestions have an internal
consistency that must at least be considered, even if they do not
address other observations of the world, such as why people universally
believe in the supernatural.

This book will challenge readers, both scientifically and in their
faith. It is quite accessible, even to the non-technical
reader. It is very well organized, concise, dotted with humor,
and truly makes a rather dull topic into an intruiging
discussion. Definitely a must-read for anyone with an interest in
Physics or beginnings.

Review: 10

The flow of the discussion is very well
done; even the necessary background digressions feel necessary
and are interesting. The writing, while not a paragon of the use
of the English language, is very readable and certainly is not overly
academic. The content is excellent, concise, accurate,
interesting, and relevant (in more ways than just the flow of
argument). My only complaint is that phrases are occasionally
repeated, as if the editing were stopped prematurely. A small
complaint, however, and really does not detract from the book. One could argue that he is a bit too consumed with eliminating the
unseemly need for God in scientific theory, but he does not let it
unduly interfere with the book, and he does have valid points. Well-worth the time spent reading, as the points he raises are sure to
be pondered by a thoughtful reader for some time.